1. Field of the Invention
The present invention relates to an electrostatic image developing toner for developing a latent electrostatic image formed in an electrophotographic method, an electrostatic recording method and an electrostatic printing method, a toner container, and a process cartridge.
2. Description of the Related Art
Dry-process developing devices using a powdery developing agent have widely been employed in image forming apparatuses such as electronic copiers, printers and facsimiles, in which a latent electrostatic image formed on a latent image bearing member is visualized with a developer to obtain a recorded image.
In recent years, color image forming apparatuses using electrophotographic process have broadly been employed, and digitized images are easily available. Thus, it is required to make an image to be printed at higher definition. While studying higher resolution and gradation of an image, as an improvement of a toner which visualizes a latent image, it has been studied to further conglobate and minimize in particle size for forming the image at high definition. And, since in the toners produced by the pulverizing methods, their conglobation and minimization are limited, so-called polymerized toners produced by a suspension polymerization method, an emulsification polymerization method and a dispersion polymerization method capable of conglobating and minimizing in particle size have been being employed.
Polymerization toners have a small particle diameter and thus, exhibit an increased adhesion force to members, which degrades transfer efficiency and causes filming. Also, the polymerization toners have a spherical shape and thus, are poor in cleanability. In addition, the polymerization methods allow toner materials of relatively low resistance to be localized near the toner surfaces. Therefore, the formed polymerization toners involve background smear due to their low chargeability. Meanwhile, in recent years, there has been increased demand for toners that attain high-quality images and have low-temperature fixing property for energy saving. Thus, a binder resin having a low melt temperature is desirably used. However, toners having a low-temperature fixing property possess newly arising problems such as generation of blocking at high-temperature, high-humidity environment, which is associated with degradation in heat resistance storage stability.
In view of this, attempts have been made to modify the surfaces of toner core particles to solve the aforementioned problems. The method for surface modification is, for example, dry methods in which fine particles are made to adhere onto the toner surfaces by the action of mechanical impact, and wet methods in which a resin dispersing agent is added to a dispersion liquid containing toner particles dispersed in a solvent, wherein the resin of the resin dispersing agent is different from the resin forming the toner particles. Regarding the dry methods, Japanese Patent (JP-B) No. 2838410 or other literatures disclose a toner including base particles and fine particles embedded in the surfaces thereof, wherein the toner is produced by adding the fine particles to the base particles heated to a temperature near their softening point, followed by stirring and mixing. Also, JP-B No. 2750853 discloses a toner including fine resin particles and core particles which are covered with the fine resin particles by the action of mechanical impact. Also, Japanese Patent Application Laid-Open (JP-A) No. 2008-191639 discloses a method of forming a coating layer by spraying a modifying material. However, any of these dry methods cannot suppress fine resin particles from being exfoliated due to, in particular, stress applied in the shear direction since the adhesion of the fine resin particles to toner particles are insufficient.
Regarding the wet methods, JP-A No. 2008-90256 discloses a method in which the surfaces of toner core particles formed of first resin particles and a colorant are partially or totally covered with second resin particles. Although this proposed method can suppress the resin particles from being exfoliated due to strong stress, the resin particles existing on the surfaces deform to cause changes in characteristics of the toner.
JP-A No. 2003-202701 discloses a method in which fine resin particles are added in advance to an aqueous phase for fusion to control the particle diameter. However, in this method, the fine resin particles are incorporated into toner core particles, and as a result, the toner core particles cannot be covered with the fine resin particles in such an amount that surface modifications are accomplished.
An object of the present invention is to provide an electrostatic image developing toner containing: toner particles; and fine resin particles attached on surfaces of the toner particles so that they are not exfoliated from the surfaces of the toner particles, thereby involving no change in toner properties during repeated use and forming high-quality images for a long period of time.